(CNN) -- The National Hurricane Center has downgraded Katia, which had been a Category 1 hurricane as it moved through the Atlantic, to a tropical storm, but it is expected to intensify after the next 24 to 36 hours.

As of 5 p.m. ET Katia was about 930 miles east of the northern Leeward Islands. Its maximum sustained winds were 70 mph, slightly below the level required to be classified as a hurricane, due to a southwesterly shear effect stemming from an upper-level low pressure system northwest of the storm, the hurricane center said.

Katia is continuing to move west at about 18 mph, and is expected to slow down and begin a gradual turn to the northwest, according to shear analysis by the hurricane center.